The optimal interval between doses of an mRNA COVID-19 vaccine is two months or eight weeks. This interval applies to two and three dose primary series.
Pfizer BioNTech Comirnaty 3mcg dose is a 3-dose primary series. Each dose is given two months (56 days) apart.
Moderna Spikevax 25 mcg is a 2-dose primary series. Each dose is given two months (56 days) apart.
There is no mixing of COVID-19 vaccine products from different manufacturers (either Pfizer or Moderna) for children six months to five years; however, if a child turns five and has not completed the series, they will be provided with the higher dose product appropriate for their age.
Children six months to under five years of age getting a COVID-19 vaccine (either Pfizer or Moderna) should not get a non-COVID-19 vaccine at the same time. A COVID-19 vaccine should be administered at least 14 days before or after getting a non-COVID vaccine (ex. flu shot).
Source: Ottawa Public Health